1. Field of the Invention
The present invention relates to an adapter for an interchangeable lens, for establishing a connection between a video signal processing system for a video camera capable of automatically controlling exposure and an interchangeable lens system for a still camera capable of automatically controlling exposure.
2. Related Background Art
Recently, there has been disclosed a lens system for a video movie system, which is different from an ordinary system composed of integrating a camera and a lens and which is capable of using a variety of interchangeable lenses. As an interchangeable lens system of the type described above, a system for a still camera such as a single-lens reflex camera has been known and a variety of lenses including special lenses for a variety of purposes have come into the market. However, since use of the interchangeable lens system is in the early stage and therefore its market has not been established yet, it is not practical that a variety of special lenses which characterizes the interchangeable lens system are manufactured in the early stage of the promotion of the video movie system. Therefore, it is effective to utilize the conventional interchangeable lenses for a still camera for a single-lens reflex camera. In a case where the video movie camera and the interchangeable lens for a still camera are connected to each other, a conversion adapter must be used because of the following reasons (a) to (c):
(a) Since the mount for the interchangeable lens system for the video movie and that for the interchangeable lens system for the still camera are different from each other, a proper adaptation means for them must be employed.
(b) Since the video movie camera and the still camera have different distances between the imaging surface and mount position, the difference in the optical passage must be aligned.
(c) Since the interchangeable lens system for the video movie and the interchangeable lens system for the still camera have different communication formats for transmitting/receiving various data required to perform the control and as well as the data format/control format are different, they must be adapted to each other.
The video movie camera and the still camera are respectively arranged to be significantly different from each other in their status, the imaging status and the functions. Therefore, also the AE (Automatic Exposure) control method is different between the video camera and the still camera. Then, the AE control method will now be described schematically.
First, the AE control method employed in a conventional camera integrated type VTR will now be described with reference to FIG. 1. Imaging light made incident through a lens optical system 1 is first subjected to a light quantity adjustment in an iris diaphragm 2 before an image of a subject is formed on an image pickup element 3, the image of the subject being then photoelectrically converted on the image pickup element 3. A signal obtained from the image pickup element 3 is converted into a TV composite video signal by a camera signal processing circuit 4 and a camera encoder 5 before it is transmitted to outside. At this time, brightness signal Yxcex3 obtained from the camera signal processing circuit 4 is subjected to an integral process in an integrator 6 before a differential signal denoting the level difference from a reference level supplied from a reference value generating circuit 19 is generated by a calculator 18. The differential signal thus-generated is, as an AE control signal, transmitted to a driver 13 so that the iris diaphragm (a diaphragm mechanism for adjusting exposure) is controlled via an actuator 14.
Then, an AE control method employed in a VTR of an interchangeable lens method will now be described with reference to FIG. 2. Referring to FIG. 2, a right portion with respect to a mount portion MT designated by a central alternate long and short dash line forms a camera unit CM, while the left portion forms a lens unit LS. An image of a subject formed on an imaging surface of the image pickup element 3 after it has passed through the iris diaphragm 2 is photoelectrically converted by the image pickup element 3 before it is transmitted as an image signal. The image signal supplied to the camera signal processing circuit 4 from the image pickup element 3 is subjected to a xcex3 (gamma) conversion or the like so that it is fetched as a video signal composed of color signal C and brightness signal Yxcex3 before it is, in the form of a composite video signal, transmitted outside from a camera portion via camera encoder 5 arranged to act in accordance with the NTSC method. The brightness signal Yxcex3 transmitted from the above-described camera signal processing circuit is supplied to the integrator 6, an amplifier (AMP) 7 and a DC level shift circuit 8 which constitute an AE circuit so that the AE control signal for controlling the iris diaphragm 2 in such a manner that proper exposure can be obtained is generated. In the above-described AE circuit, the brightness signal Yxcex3 is integrated by the integrator 6 before it is amplified to a predetermined level by the amplifier 7. Then, the amplified signal is made to be the above-described reference level by a DC level shift circuit 8. A method of setting AE control data in accordance with the level difference from the above-described reference level is, as described later, arranged in such a manner that the amplifier 7 and the DC level shift circuit 8 are adjusted so as to generate communication data, for example, as shown in FIG. 3, in accordance with the brightness difference of the received signal. A signal generated in the AE circuit is converted into a digital signal by an A/D converter 9 before it is supplied to a microcomputer 10 for the camera so as to be transmitted to the lens unit LS as the AE control signal via a data communication passage 21 at predetermined timing. At this time, the data communication passage 21 is connected to a microcomputer 11 for the lens so that all of communication data items are received by the microcomputer 11 for the lens before the communication data is converted into an analog signal by a D/A converter 12. Then, the analog signal is supplied to the driver circuit 13. Then, the iris diaphragm 2 is controlled via the actuator 14. FIG. 3 is a table which illustrates representative value of AE control data to be transmitted to the lens unit LS which is assigned by, for example, 8 bits (256 steps). As shown in FIG. 3, each level difference is expressed by an EV (diaphragm) value such that an instruction is made in a case where the value is+1 EV to perform a diaphragm of 1 EV (so-called xe2x80x9cfor one diaphragmxe2x80x9d) with respect to the optimum exposure. Furthermore, a reference value for the AE control is determined to be 32 in this case and the action of the iris is inhibited. In the portion including the lens, control data transmitted from the portion including the camera is again converted into an analog signal by the D/A converter 12 so as to drive the actuator 14 via the driver 13. As a result, the iris diaphragm 2 is operated. As described above, the control signal including a control signal for stopping the operation of the iris in accordance with the level of the video signal is, as AE control information, formed into a digital code so as to be transmitted. Therefore, the apparent gain different of the camera can be neglected and as well as the difference in the dynamic range of the camera can be made to be regardless. Furthermore, since the reference values are unified in accordance with a predetermined code, compatibility can be maintained as desired.
Finally, the AE control method employed in a still camera will now be described with reference to FIG. 4. Imaging light made incident upon the lens optical system 1 is first subjected to a process in which the quantity of light is adjusted by the iris diaphragm 2 similarly to the above-described structure. Then, it is supplied to a photometry element 3A for performing a part and average photometry and a photometry element 3B for performing a spot photometry. The outputs from the photometry elements 3A and 3B are respectively amplified by the amplifiers 7A and 7B before they are supplied to a photometry circuit 23. In the photometry circuit 23, a photoelectric current is converted into voltage obtained by logarithmic compression so as to be supplied to the microcomputer 10 for the camera. In the microcomputer 10 for the camera, an exposure calculations for obtaining the proper exposure is performed in accordance with a variety of AE modes (the shutter priority AE mode, the diaphragm priority AE mode, depth priority AE mode). The result of the above-described calculations are obtained as a value which corresponds to the difference between the photographic diaphragm and an open diaphragm, that is, the number of diaphragm steps. The number of diaphragm steps thus-obtained is supplied to the microcomputer 11 for the lens included in the lens unit LS via the data transmission passage 21.
The number of diaphragm steps supplied from the portion including the camera is converted into the number of steps of a stepping motor (M) 20. As a result, a stepping motor 14 is rotated via the driver 13 in accordance with the number of steps. As a result, the iris diaphragm 2 is opened/closed so that exposure is controlled. At this time, the relationship between the stepping motor 20 and the iris diaphragm 2 is arranged in such a manner that the diaphragm is changed by, for example, xe2x85x9 step when the rotor of the stepping motor 14 is rotated by one pitch.
According to the control method thus-constituted, the AE control method employed in the interchangeable lens system for the video movie camera is arranged in such a manner that the difference between the present light quantity and the reference light quantity is transmitted to the lens portion. In the lens portion, the diaphragm mechanism is driven in an analog manner from the present position in accordance with the difference value thus-transmitted so that the light quantity is controlled. Finally, a control is performed in such a manner that the reference light quantity and the actual incidental light quantity are made to be the same. On the other hand, the AE control method for the interchangeable lens system for the still camera is arranged in such a manner that the difference between absolute value information about the present diaphragm in the camera portion and absolute value information about the desired diaphragm is converted in accordance with the drive means (for example, the number of pulses of the pulse motor) for the lens. Then, data obtained by the above-described conversion is transmitted to the lens portion before the lens portion controls the light quantity by driving the diaphragm mechanism by an instructed number of the pulses in a digital manner so that a diaphragm (quantity of light) required by a user is realized. Therefore, AE control data from the camera in the interchangeable lens system for the video movie camera cannot be directly used as AE control data for controlling the interchangeable lens in the interchangeable lens system for the still camera. Therefore, there arises a problem in that the AE control cannot be performed.
To this end, an object of the present invention is to provide an adapter device enabling a lens system except for a lens system for a video camera, for example, a lens system for a still camera to be connected to a video camera.
Another object of the present invention is to provide an adapter for an interchangeable lens for a camera capable of enabling two different AE control methods to match with each other, enabling an interchangeable lens of an interchangeable lens system for a still camera to be used in an interchangeable lens system for video camera, and satisfactorily performing an AE control.
In order to achieve the above-described object, according to one aspect of the present invention, there is provided a conversion adapter device for establishing a connection between the body of a camera and a lens unit each having different control methods, the conversion adapter device comprising: signal receiving means for receiving a control signal transmitted from the body of the camera; computing means for converting the form of the control signal thus-received into a form which matches with the control method for the lens unit; and transmission means for transmitting a signal denoting the result of computing transmitted from the computing means to the lens unit.
According to another aspect of the present invention, there is provided a conversion adapter device for a camera comprising signal conversion means for converting an automatic exposure control signal generated from the output from a video signal processing circuit of a video camera which is capable of performing an automatic exposure control into an automatic exposure control signal which is adapted to an interchangeable lens system for a still camera capable of performing an automatic exposure control.
As a result of the function of the signal conversion means, the interchangeable lens for the still camera can be used similarly to a manner for using the interchangeable lens for the video camera when viewed from the video camera. Therefore, the difference in the lens can be overcome. Furthermore, interchangeable lens for the still camera acts as if it processes data supplied from the still camera so that it can be used while eliminating a necessity of modifying it to serve as the lens.
A third object of the present invention is to provide an adapter for an interchangeable lens of a camera capable of performing a proper control regardless of the difference in the characteristics of each lens unit when the body of the camera and the lens unit are coupled to each other via the adapter in a case where there are a plurality of kinds of the control portion for the lens unit.
In order to achieve the above-described object, according to another aspect of the present invention, there is provided a conversion adapter device for an interchangeable lens system capable of attaching/detaching a lens portion to and from a camera portion, the conversion adapter device for an interchangeable lens system comprising a plurality of conversion means for converting information about the operational position of exposure control means in the lens portion into a form which can be discriminated by the camera portion when the camera portion and the lens portion have different exposure discrimination methods for discriminating the the operational status of the exposure control means; and selection means for selecting any one of a plurality of the conversion means in accordance with specific information about the lens.
As a result of the signal conversion means for the above-described adapter, conversion methods which have been adjusted and adapted to each actuator are respectively provided so as to be selectively used so that a variety of controls such as the AE control of a variety of lenses can be performed in a case where a variety of lenses each having different formats are used.
A fourth object of the present invention is to provide a conversion adapter device for an interchangeable lens arranged in such a manner that it has a plurality of data conversion tables for forming drive information which corresponds to the difference in the characteristics of the lens drive portion and the adapter portion selects a proper conversion table in accordance with information about the connected lens, whereby a proper AE control can be performed for the attached lens and therefore an excellent image quality can be obtained even if any one of a variety of lenses is attached.
Other and further objects, features and advantages of the invention will be appear more fully from the following description.